Snap Plugin Library for C++

This is a library for writing plugins in C++ for the Snap telemetry framework.

Snap has four different plugin types. For instructions on how to write a plugin check out the following links to example plugins:

• collector,
• streaming-collector.
• processor,
• publisher.

Before writing a Snap plugin:

• See if one already exists in the Plugin Catalog
• See if someone mentioned it in the plugin wishlist

If you do decide to write a plugin, open a new issue following the plugin wishlist guidelines and let us know you are working on one!

Brief Overview of Snap Architecture

Snap is an open and modular telemetry framework designed to simplify the collection, processing and publishing of data through a single HTTP based API. Plugins provide the functionality of collection, processing and publishing and can be loaded/unloaded, upgraded and swapped without requiring a restart of the Snap daemon.

A Snap plugin is a program that responds to a set of well defined gRPC services with parameters and returns types specified as protocol buffer messages (see plugin.proto). The Snap daemon handshakes with the plugin over stdout and then communicates over gRPC.

Snap Plugin C++ Library Examples

You will find example plugins that cover the basics for writing collector, processor, and publisher plugins in the examples folder.

Building libsnap:

Requiered tools:

• autoconf
• automake
• curl
• g++
• libtool
• make

Dependencies:

• Boost (Github), latest version (currently 1.68)
• gRPC and Protobuf (Github), latest version (currently 1.15.1)
• cpp-netlib (Github), latest version (currently 0.13.0)
• spdlog (Github), latest version (currently 1.2.0)
• nlohmann json (Github), latest version (currently 3.3.0)

Boost

You can either download precompiled Boost libraries and headers or build them from source.

Versions 1.57 to latest (1.68) are supported.

Snap requires headers of Boost.Program_options, Boost.Algorithm, Boost.Any and Boost.Filesystem (the latter two may be replaced by their C++17 STL equivalents), and static libraries of boost_program_options, boost_system and boost_filesystem.

gRPC and Protobuf

It is recommended to build gRPC and Protobuf from source to avoid dependency conflicts.

Versions 1.0.1 to latest (1.15.1) are supported.

To install GRPC

git clone https://github.com/grpc/grpc
cd grpc
git checkout tags/v1.15.1
git submodule update --init
make
[sudo] make install

To install Protobuf (Google Protocol Buffers):

Snap plugin library for C++ depends also on protobuf library. As it is already in gRPC dependencies, you can install it like:

cd grpc/third_party/protobuf
[sudo] make install

Then you have to generate Snap's plugin Protobuf interface:

cd snap-plugin-lib-cpp/src/snap/rpc
protoc --cpp_out=. plugin.proto
protoc --grpc_out=. --plugin=protoc-gen-grpc=/usr/local/bin/grpc_cpp_plugin plugin.proto

Be careful to use the protoc executable that was built previously! It should be in /usr/local/bin/.

cpp-netlib

Version 0.13.0 (latest) is supported.

git clone https://github.com/cpp-netlib/cpp-netlib
cd cpp-netlib
git checkout tags/cpp-netlib-0.12.0-final
git submodule update --init

Then, create a cpp-netlib-build directory next to the cloned repository:

cd ..
mkdir cpp-netlib-build
cd cpp-netlib-build
cmake ../cpp-netlib
make
[sudo] make install

Asio

For cpp-netlib version 0.12.0, Asio headers need to be installed as well. This is not needed for other versions of cpp-netlib.

As Asio is already in cpp-netlib dependencies, you can install it like:

cd cpp-netlib/deps/asio/asio
./autogen.sh
./configure
make
[sudo] make install

And then build cpp-netlib again

Other versions of cpp-netlib use Boost.Asio, which is installed with Boost.

spdlog

Versions 0.13.0 to latest (1.2.0) are supported.

git clone https://github.com/gabime/spdlog
cd spdlog
git checkout tags/v1.2.0
[sudo] cp -r ./include/spdlog /usr/local/include

JSON

Versions 2.0.9 to latest (3.3.0) are supported.

wget https://github.com/nlohmann/json/releases/download/v3.3.0/json.hpp
[sudo] cp json.hpp /usr/local/include/json.hpp

Once the above dependencies have been resolved:

First, execute ldconfig /usr/local/lib/ to allow ld to look for installed libraries in /usr/local/lib. Then you can build the Snap library:

./autogen.sh
./configure
make
[sudo] make install

libsnap (and all previous dependencies) are installed into /usr/local/lib, which not all linkers use when searching for shared objects. Using the --prefix=/usr switch when running the configure script will place the resulting libraries into /usr/lib, for example.

To clean up and rebuild use:

make clean
git clean -xdf  # warning! This deletes all dirs and files not checked in. Be sure to check in any new files before running `git clean`.